This invention relates to improvements in a dental handpiece for the treatment of root canals, and more particularly in a dental handpiece for the enlarging of root canals.
For the treatment and in particular for enlarging of root canals, a dental tool must be driven to rotate alternately in one direction and in the other direction coupled with an up and down movement.
According to the conventional dental handpiece, a driving shaft rotatably held in a sleeve is fixed with a circular disc which carries around its periphery a pinion lug, and perpendicularly to the axis of the driving shaft, and in the interior of a case of a drilling tool is mounted a hollow circular cylinder having a longitudinal guide slot. The hollow cylinder is made integral with the tool, while the pinion lug is mounted in such a way as to slide alternatively or reciprocally in the guide slot when the disc rotates continuously. Through the continuous rotation of the disc, reciprocating rotary movement is achieved around a perpendicular axis of the cylinder bearing so that the drilling tool may rotates about every one quarter turn.
It has been found, however, that the pinion lug coupled into the longitudinal slot of the cylinder reciprocates in direct contact with the inner wall of the slot so that the unsmooth alternate rotational movement is effected to cause severe wearing out both for the longitudinal guide slot and the pinion lug. In addition, the pinion lug may unhook easily out of the longitudinal guide slot at the two extreme positions of the slot.
A principal object of this invention is to provide a dental handpiece for the treatment of root canals whereby dental tools such as drills, buffers, reamers, or the like can be effectively driven to rotate alternately in one direction and in the other direction coupled with an up and down movement.
Another object of this invention is to provide a dental handpiece for the treatment of root canals whereby a rotating driving shaft is indirectly coupled with a hollow cylinder holding a dental tool by means of a roller bearing such as a ball bearing rotatably held in the longitudinal slot of the hollow cylinder so as to achieve smooth alternating rotational movement.
A further object of this invention is to provide a dental handpiece whereby abrasion of the roller bearing and of the pinion lug as well as a possible unhooking of the pinion lug can be prevented at the two extreme positions of the slot.
A further object of this invention is to provide a dental handpiece which will enable the dentist to carry out a treatment with tactile sense of his fingers.
A still another object of this invention is to provide a device suitable for the aforementioned purposes which will be comparatively simple in construction and at the same time desirably rigid, strong and durable.